Thanks for help, guys! I've implemented the functionality I was looking for. I've found the corresponding loop in archive-product.php and as was suggested by JapanGuy, I've added a simple "if i equal let's say 5 then echo < li>[Custom block]< /li>" .
The original snippet from archive-product.php:
<?php woocommerce_product_loop_start(); ?>
<?php woocommerce_product_subcategories(); ?>
<?php while ( have_posts() ) : the_post(); ?>
<?php wc_get_template_part( 'content', 'product' ); ?>
<?php endwhile; // end of the loop. ?>
<?php woocommerce_product_loop_end(); ?>
Modified code with inserted custom block:
<?php woocommerce_product_loop_start(); ?>
<?php woocommerce_product_subcategories(); ?>
<?php while ( have_posts() ) : the_post(); ?>
<?php
if ($i == 5) {
echo "<li>[Custom block]</li>";
}
$i++;
?>
<?php wc_get_template_part( 'content', 'product' ); ?>
<?php endwhile; // end of the loop. ?>
<?php woocommerce_product_loop_end(); ?>
Im such simple way I can add any content to the created [Custom block] and have an usual products grid with extra custom designed block. I'm not very experienced programmer, so probably my code is not perfect, but it works. Thanks!